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SEROUS MEMBRANES, BY E. KLEIN. 



superjacent layer of cell substance to project at this point. The 

 more regularly the cell is otherwise fashioned, by so much the 

 more does the nucleus approximate the spheroidal form. The 

 endothelium on the mesentery of the Rabbit is very regularly 

 polyhedral, as is also that of the newly born child, that of the 

 peritoneum investing the stomach and intestine of the Frog 

 and Cat, and of the thoracic surface of the tendinous centre 

 of the Guinea-pig. 



Amongst the most irregular in form are the cells of the 

 mesentery of the Frog, and in part also of the Cat. They are 

 here always quite irregularly shaped, forming more or less 

 elongated plates, constantly presenting irregular projections, 

 and hence it results that the boundary lines of two adjoining 

 cells are always more or less sinuous. The elongated cells of 

 the two surfaces decussate in the direction of their length in 

 the same manner as those of the opposite walls of a large 

 lymphatic. 



The nucleus of these endothelial cells rarely occupies a 

 central position, but is usually oblong, and sometimes exhibits 

 constrictions that affect either one half of the nucleus only, or 

 its entire circumference; and indeed it is not infrequent to 

 meet with elongated cells presenting several projections at the 

 poles, and containing two nuclei. 



On the pleura, the pericardium, and the central tendineum 

 of the diaphragm, besides regular polyhedric cells, we meet 

 also with more or less irregularly formed ones, presenting tri- 

 angular and more or less elongated rhomboidal forms. The 

 greatest variation also occurs in regard to the size of the cells 

 and the extent of their periphery. Sometimes they are of the 

 same magnitude over surfaces of considerable extent, some- 

 times a few groups of disproportionately small cells are 

 found irregularly scattered, sometimes with and sometimes with- 

 out intermediate forms. The latter arrangement is beauti- 

 fully shown in the pericardium of the Cat, as well as on 

 the pleura intercostalis (3), and upon the lymphatics on the 

 abdominal surface of the peritoneum (4). The form of the 

 endothelial cells, as exhibited in preparations stained with 

 nitrate of silver, varies from point to point ; but in the 

 mesentery of the Frog and Cat, on the abdominal surface of 



